The use of a cluster ion beam for processing surfaces is known (see for example, U.S. Pat. No. 5,814,194, Deguchi et al.) in the art. In this description, gas-clusters are defined as nano-sized aggregates of materials that would be gaseous under conditions of standard temperature and pressure. Such gas-clusters typically consist of aggregates of from a few to several thousand molecules loosely bound to form the cluster. The clusters can be ionized by electron bombardment or other means, permitting them to be formed into directed beams having controllable energy. Such ions each typically carry positive charges of q·e (where e is the electronic charge and q is an integer of from one to several representing the charge state of the cluster ion). Non-ionized clusters may also exist within a cluster ion beam. The larger sized cluster ions are often the most useful because of their ability to carry substantial energy per cluster ion, while yet having only modest energy per molecule. The clusters disintegrate on impact, with each individual molecule carrying only a small fraction of the total cluster ion energy. Consequently, the impact effects of large cluster ions are substantial, but are limited to a very shallow surface region. This makes cluster ions effective for a variety of surface modification processes, without the tendency to produce deeper subsurface damage characteristic of conventional monomer ion beam processing.
Means for creation of and acceleration of a gas-cluster ion beam (GCIB) are described in the reference (U.S. Pat. No. 5,814,194) previously cited. Presently available cluster ion sources produce cluster ions having a wide distribution of sizes, N (where N=the number of molecules in each cluster ion—in the case of monatomic gases like argon, an atom of the monatomic gas will be referred to as a molecule and an ionized atom of such a monatomic gas will be referred to as a molecular ion—or simply a monomer ion—throughout this discussion).
Many useful surface-processing effects can be achieved by bombarding surfaces with GCIBs. These processing effects include, but are not necessarily limited to, cleaning, smoothing, etching, doping, and film formation or growth.
In processing workpieces with a gas-cluster ion beam, it is generally desirable to use a scanning technique to provide for uniform processing of workpieces that are larger than the GCIB cross section. In the prior art, electrostatic beam scanning has sometimes been employed to scan GCIBs across a workpiece. As the available GCIB currents have increased with improved beam generation techniques, electrostatic scanners have become less practical and it has become customary to mechanically scan the workpiece through a stationary GCIB to achieve uniform processing of large workpieces. In such cases, a workpiece (often, but not necessarily a semiconductor wafer) has been held in a holder attached to an X-Y scanning platform. These X-Y mechanical scanners have been effective for uniformly processing workpieces in ion beams. In order to achieve uniform processing, it is desirable to scan the workpiece in a raster or other pattern that forms a complete treatment pattern on the workpiece by the ion beam and wherein the pitch of the scanned pattern is fine compared to the size of the ion beam or compared to any non-uniformity of the spatial intensity of the incident ion beam spot on the workpiece. Additionally, uniformity is improved if multiple, complete scans of the workpiece are performed, thus compensating for small temporal variations in the ion beam intensity. Thus it is desirable to be able to perform rapid scanning of the workpiece in order to quickly achieve complete coverage, and if required, multiple complete scans. However, existing X-Y mechanical scan mechanisms have been relatively slow moving due to the practical difficulties involved in rapidly accelerating the masses involved. Furthermore, attempts to speed the motion by brute force techniques results in transmission of excessive vibration to the supporting members of the frame of the ion beam processing equipment, often resulting in creation of reliability problems and/or other practical problems.
Published US Patent Applications US2005/0230643A1, US2005/0232748A1, and US2005/0232749A1 all due to Vanderpot et al. describe methods and apparatus for scanning or reciprocating workpieces through an ion beam using a novel counter-rotating stator motor design for reducing transmitted vibration, while providing high scan velocities and accelerations in an arcuate scanning path. The entire contents of US2005/0230643A1, US2005/0232748A1, and US2005/0232749A1 are hereby incorporated herein by reference.
As it is often more practical to generate a GCIB processing beam along a horizontal or near horizontal trajectory, it is desirable to process workpieces such as semiconductor wafers such that the workpiece surface is in a vertical plane (and thus intercepting the ion beam at a direction approximately normal to the surface being processed) during processing. On the other hand, flat workpieces such as semiconductor wafers are often transported in standardized containers in which the workpieces are held so that their flat surfaces are substantially in a horizontal plane. It is often easier and more reliable (or otherwise desirable) to remove flat workpieces from their transport containers for loading onto a holder for processing in an ion beam by using robotic or automated handling systems that move the workpieces while maintaining them in a substantially horizontal orientation.
It is therefore an objective of this invention to provide a method for and apparatus for rapidly scanning a workpiece through an ion beam for uniform processing.
It is another objective of this invention to provide a method for and apparatus for rapidly scanning a workpiece through an ion beam, with reduced transmission of vibrations to the scanner supporting members of the GCIB processing equipment and to other portions of the GCIB processing equipment.
It is a further objective of this invention to provide methods and apparatus for horizontal loading and unloading of the workpiece onto the scanner workpiece holder, while permitting vertical orientation of the workpiece during ion beam processing.